practical volume rendering for realtime applications
DESCRIPTION
Slides for a talk I gave in October 2013 at Chaos Group's CG2 seminar in Sofia. Brief information about the state of Volume rendering for games and details about the TransVoxel algorithm by Eric Lengyel.TRANSCRIPT
Practical Volume rendering for realtime applications
Stoyan Nikolov
VIDEO
Who am I
Stoyan [email protected]@stoyannk
Co-Founder & Tech lead @ Coherent Labs
Senior Graphics dev @ Masthead Studios
Senior dev @ Eutelia
Why use Volume rendering at all?
What is Volume rendering?
Types of Volume rendering techniques
Practical (today) rendering techniques
Overview
Why Volume rendering
• Allows us to see „inside“ an object
• Medical imaging
• Industry
• Biology
Why Volume rendering - Games
Freedom of form
Why Volume rendering - Games
Destructability
EverQuest Next by Sony Online Entertainment
Why Volume rendering - Games
Procedural generation
Volume rendering - Input
Usually discrete volume elements — voxels
Direct rendering in RT
• Ray-marching distance fields• Gigavoxel• Sparse voxel octrees (SVO)• SVO for Global Illumination
slisesix demo by rgba
Unreal Engine 4 by Epic Games
• Create a polygon mesh• GPUs are designed for polygons• Other subsystems usually expect polygons
Indirect rendering for RT
Basic algorithms
Marching cubes / tetrahedra / MC 33
Realtime requirements
• We want to support very large meshes
• Level of Detail (LOD) required
• Difficult with MC
• Transvoxel designed to solve this
Transvoxel
• Outline in Eric Lengyel’s PhD thesis
• Designed for RT applications
• Originally implemented in C4 Engine
Transvoxel overview
• Based on MC
• Extend equivalence classes
Basic Algorithm
• Subdivide grid in blocks (once)• Polygonize blocks (once)• Decide blocks to draw and LOD (per-frame)• Draw relevant blocks (per-frame)
The LOD solution
• Introduce “transition cells” between levels• Restricted octree for rendering• Identify neighbors and draw correct transitions
Transition cells
Important detail
Surface shifting
Texturing
• Per-voxel material Id → Texture Ids• Triplanar projection• Two sets of textures are blended for better transitions
Parallelism
• Embarrassingly parallel
• Relatively easy for GPGPU
• Parts can be re-computed independently
DEMO
Dual contouring
• Solves the sharp edges• Works on hermite data sets
VoxelFarm engine by Voxel Farm Inc.
Comparison
• MC-based algorithms
faster
require less memory
• Dual algorithms support more geometries
Potential headaches
• Memory consumption
• Correct implementations sometimes tricky
• Texturing
